It is well known that springs can be manufactured from a variety of materials including metals and plastics.
The properties of springs are wide-ranged and are characterized by parameters including configuration, diameter, length, helical angle or pitch, diameter and materials. These factors and others will establish the performance of a particular spring design.
For example, one key parameter of a spring is its rate. The rate of a spring is the change in the force it exerts, divided by the change in deflection of the spring. That is, the rate of a spring is the gradient of the force versus deflection curve. For an extension or compression spring, this will normally be expressed in lbf/in or N/m. The inverse of spring rate is compliance which is the inverse of rate. That is, if a spring has a rate of 10 N/mm, it has a compliance of 0.1 mm/N. The stiffness (or rate) of springs in parallel is additive, as is the compliance of springs in series.
Ideally, any spring will have a highly repeatable and reliable performance over many cycles to ensure consistent performance in its application. For example, in certain applications a spring may be termed “successful” if 100,000 maximum stroke cycles are demonstrated without failure. In other applications, other parameters such as lower weight and increased dampening may be desirable in addition to reliability.
In the specific case of the automotive industry, currently utilized metal springs are limited in certain applications by properties such as weight and spring dampening. For example, in a high performance application such as a race car, there is a need for the lowest weight solution for each component on the race car.
Further still, in an automobile engine, valve springs can limit the engine maximum speed by their natural frequency. That is, once the valve spring reaches its natural frequency due to the speed of the engine, the valve “floats” which prevents the proper motion of the valve thereby resulting in inefficient use of fuel into the engine combustion chamber and/or exhaust gases expulsion.
Further still, steel springs are subject to other disadvantages such as corrosion and electrical and thermal conductivity thus making them unsuitable for particular applications.
As a result, there has been a need for improved springs in which weight, performance and other properties are improved while otherwise maintaining similar properties to existing metal springs.